1. Field of the Invention
The present invention relates generally to a dielectric filter having at least one dielectric resonator, the dielectric resonator having an internal conductor which is formed within a dielectric block and an external conductor which is formed on the outside of the dielectric block.
2. Description of Related Art
Filters for use in, for example, the microwave band, include a dielectric filter, in which a resonator electrode is formed within a dielectric block and an earth electrode is formed on the outside face of the dielectric block, and a so-called Triplate(trademark) type of dielectric resonator with strip lines located opposite to each other on respective main faces of a dielectric substrate, the strip lines serving respectively as a signal strip line on one main face and an earth electrode on the other main face.
FIG. 39 shows an exploded perspective view of the construction of the conventional general dielectric resonator using a dielectric block. In FIG. 39, reference numeral 40 is a six-sided dielectric block with three internal conductor holes 46, 47, 48 each having an internal conductor provided therein and coupling holes 49, 50 which are provided between the internal conductor holes 46, 46, 48. The internal conductors are formed on the inside surfaces of the internal conductor holes 46, 47, 48, and an external conductor 51 is formed on five faces of the dielectric block 40 except for an open face 52. Reference numerals 53, 54 are so-called resin pins, each being composed of resin portions 53a, 54a and signal input, output terminals 53b, 54b. Two resin pins 53, 54 are inserted into the internal conductor holes 46, 48 from the open face side of the dielectric block 40 so that the terminals 53b, 54b are coupled capacitively to the corresponding internal conductors within the internal conductor holes 46, 48. Reference numeral 55 is a case for retaining the dielectric block 40 and the resin pins 53, 54 and also, for covering the open face portion of the dielectric block 40. The resin pins 53, 54 are respectively inserted into the dielectric block 40 so as to be covered by the case 55, and also, the whole arrangement is integrated by soldering the case 55 to the external conductor 51. For mounting the dielectric resonator on a circuit substrate, the projecting portions 55a, 55b of the case 55 function as an earth terminal.
As shown in FIG. 39, many components such as input, output terminals 53b, 54b, case 55 and so on, are necessary if a plurality of resonators are to be formed in a single dielectric block. The assembly steps therefore become complicated. Moreover, it is necessary to attach a lead wire to the component when mounting the completed product on a circuit substrate. Therefore, surface mounting cannot be effected, as it can with other electronic components, so as to mount a plurality of these completed products on the same circuit substrate. Thus, it is difficult to provide an assembly which is low in height.
Further, if the case 55 is not used, the external conductor 51 of the dielectric block 40 is directly connected to the earth electrode on the circuit substrate, so that the open face 52 is exposed, and thus, electromagnetic field leakage occurs at this location. Thus, when a metallic object approaches the open face 52, the metallic object influences this electromagnetic field. Further, since the resonator is coupled with this electromagnetic field, the desired characteristics of the dielectric resonator cannot be obtained.
Accordingly, the present invention has been developed with a view to substantially eliminating the above discussed drawbacks that are inherent in the prior art, and has for its essential object to provide an improved dielectric resonator.
Another important object of the present invention is to provide an improved dielectric resonator which can be surface mounted on the circuit substrate without the use of resin pins and a case as individual parts, as required by the prior art device shown in FIG. 39.
Still another object of the present invention is to provide a dielectric resonator in which electromagnetic field leakage between the inside and the outside of the resonator near the opening portion is reduced, so as to remove the problem caused by the above described electromagnetic field leakage.
A further object of the invention is to provide a method by which a resonator can be adjusted with ease and accuracy so as to have desired characteristics.
A further object of the present invention is to provide a dielectric resonator in which it is easier to obtain floating capacitance by a comparatively simple working or molding operation.
In accomplishing these and other objects, a dielectric resonator in accordance with a first aspect of the invention is provided having a non-conductive portion formed in at least one internal conductor near one end face of the above described dielectric block, and signal input, output electrodes for providing capacitive connection with the above described internal conductor are provided on the outer surface of the dielectric block. The dielectric resonator includes at least one internal conductor hole, or a plurality of internal conductor holes, within the dielectric block, the external conductor being formed on the outside of the above described dielectric block.
In the dielectric resonator of the first aspect of the invention, the non-conductive portion in the internal conductor hole is provided near one end of the at least one hole, or the plurality of holes, of the dielectric resonator, and the signal input, output electrodes effect capacitive connection with the internal conductor. A tip end capacitance is created at the non-conductive portion in the at least one internal conductor hole so as to provide comb-line coupling or interdigital coupling between the adjacent resonators. In this construction, the conductor is present on each end face of the dielectric body, so that large electromagnetic field leakage is avoided.
As coupling holes are not required, the whole arrangement can easily be made smaller in size. As the signal input, output electrodes are provided so as to provide a capacitive connection with the internal conductor, the signal input, output terminals are not required to be separate, individual parts. The external conductor can be connected with the earth electrode on the circuit substrate by surface mounting, and also, the signal input, output electrodes can be similarly connected with the signal line on the circuit substrate.
A dielectric resonator of a second aspect of the invention is characterized in that the dielectric filter described in accordance with the first aspect of the invention is an approximately six-sided unit and the above described signal input, output electrodes may be formed only on a circuit substrate mounting face thereof.
In the dielectric resonator of the second aspect of the invention, the above described signal input, output electrodes may be formed only on the mounting face which is to be mounted to the circuit substrate. Therefore, electromagnetic field leakage of the signal input, output electrodes is reduced when the dielectric resonator is mounted on the substrate, the resonator characteristics are less changed by the influence of external metallic objects, and no unnecessary connections with other circuit portions are required, thereby simplifying the circuit design and assembly operation. Further, pattern formation on the circuit substrate is simplified, because the signal input, output electrodes are formed within one plane.
A dielectric resonator of a third aspect of the invention has a plurality of internal conductors formed in holes within a dielectric block, an external conductor is formed on the outside of the dielectric block, one end face of the above-described dielectric block being a short-circuit face where the internal conductors within the holes are short-circuited, the other end face of the dielectric block being referred to as an open-circuit face. A portion of a resonator hole where no internal conductor is formed is provided near the open-circuit face so as to provide an open-circuited end of said resonator. Signal input and output electrodes for providing capacitive connections with the above-described conductors are provided on one portion of the external conductor. Moreover, portions of the external conductor and the dielectric are removed from portions of the above-described short-circuit face, the above-described open-circuit face, or both the faces.
In the dielectric resonator of the third aspect of the invention, as just described, there are portions at one portion of the open-circuit face where the external conductor and the dielectric are not formed, near the portion of the resonator hole where no internal conductor is provided; or on the short-circuit face; or on both the faces. If portions of the conductor and the dielectric are removed from the open-circuit face, near where a portion of the internal conductor is not provided, the resonance frequency of the resonator can be raised. If the conductor and the dielectric are removed between adjacent holes in the short-circuit face, the coupling between the resonators is weakened, and also, the resonance frequency of the resonator can be lowered. If the conductor and the dielectric are removed around the holes, except for between the adjacent holes, the resonance frequency of the resonator can be lowered. Therefore, adjustments of the coupling and the frequency can be easily effected without measures such as the addition of conductive coatings and so on in the portion of the hole where no internal conductor is provided.
A dielectric resonator of a fourth aspect of the invention has internal conductor holes in the dielectric block, each having an internal conductor formed on the inside surface thereof, an external conductor is provided on the outside face of the dielectric block, and hollows in at least one end face of the dielectric block are centered on the internal conductor holes, so that the internal conductors are removed near the above described hollows. Due to the hollows centered on the internal conductor holes in at least one end face of the dielectric block, the open-circuited ends of the internal conductors are formed at locations spaced from the end face, so that electromagnetic field leakage between the inside and the outside of the dielectric resonator is lessened and stable resonator characteristics are obtained.
In a dielectric resonator of a fourth aspect of the invention, the non-conductive portions in the internal conductor holes are formed by removing one portion of the internal conductor from a location near the end face of the dielectric block but spaced from the end face. In the dielectric resonator of the fourth aspect of the invention, as the non-conductive portion is spaced from the end face of the resonator, the electromagnetic field leakage is further reduced.
In a characteristic adjusting method for a dielectric resonator according a fifth aspect of the invention, each of the plurality of resonator holes has an inner surface with substantially constant cross-sectional shape along its axial direction and an internal conductor provided on the inner surface, a non-conductive portion being provided at the inner surface of the hole, a surface of the non-conductive portion being substantially flush with the inner surface of the hole, the method comprising the steps of initially forming each internal conductor over an entire length of the inner surface of the hole, and thereafter removing, for example by grinding, a portion of the inner conductor in order to form the non-conductive portion.
According to a sixth aspect of the invention, the characteristic adjusting method of the fourteenth aspect of the invention may comprise the additional step of forming the dielectric body with first and second portions on its outer surface which are spaced away from the hole by different respective distances.